Wet Tire Sanding Station

[HO RacePro]

This particular project had been hanging fire for maybe a year? I'm not sure what got me off the dime, but I decided to work on it some more and get it operational.



That is, a wet sanding station for 1/32nd tires, with the ability to handle a complete wheel/tire/gear/bushings/axle assembly. In this case one off of a Carrera slotcar. Specifically for a Carrera rear axle assembly because everything is pressed onto a knurled axle and cannot be disassembled/reassembled without damaging the wheels and crown gear.

The Carrera tires were already glued and trued. Truing done on my Professor Motor machine. The wet sanding was done to polish the tires. The Professor Motor truing station spins the tires too fast to do a proper job of polishing them. And popular wisdom is the Carrera tires need to be polished to get maximum grip.

So the wet sanding station was designed with a shallow pan to hold a wet grade of sandpaper -- in this case 400 grit -- and a few cc's of water/dishsoap solution. Said dishsoap was Dawn brand dishwashing liquid.

The dishsoap solution -- mostly water -- serves two purposes. It keeps the tires cool plus it lubricates the contact surface. Both prevent the stick/slip that causes chatter marks.

The drive is by a 12 volt gearmotor that runs at approximately 100 RPM. The low speed prevents the dishsoap solution from foaming and splashing. The same pulley that came with my Professor motor machine was used here, instead of a timing pulley I'd modified, because the timing pulley was too wide to fit. So the drive belt was an O-ring rather than the timing belt I would have used otherwise. I had to use a very light contact pressure to keep the O-ring from slipping. Contact pressure, by the way, was dialed in using the micrometer feed that lowers the plate that supports the drive and axle.

One feature I would add to this wet sanding station -- something I hadn't come up with back when I designed this thing -- is a shifter mechanism. That modification is in the works.

For now, the following video shows how the whole business performs...

And here is the finished product, below.

[dw5555]

Wow, that is SLOW..

[SuperSlab]

I am curious: I am not sure if it just the photograph, but the tyres really do not look as smooth as I would have expected them to be from a wet polishing. Is it just an illusion in the photograph or does it look like that in real life? I typically polish both urethanes and NSR rubber tyres on a Tire Razor with just a drop or so of water per tyre on 600 wet/dry paper and it generally looks a lot smoother than your photograph would suggest.

Another question: how do you ensure that the alignment of the axle is identical in your truer and your polisher? I would expect even a small angular difference between the two machines would require a fair bit of "diameter correction" of one tyre on the polisher.

[HO RacePro]

Good questions. I haven't really had much time to experiment with the machine. I was using 400 grit, not 600 grit, and I may not have polished the tires long enough. When I add a shifter it may make a difference.

As for axle alignment, that is not easy to make square, let alone make identical between two machines. Let's just say I tried my best, and will be trying to find ways to make it better. Those tires do look like they got equal treatment. And the car does run well on the track.

I'm curious how well your "drop or so of water" lubricates things. At Tire Razor RPM's I'd think that drop or so would get flung off quickly.

[SuperSlab]

I use quite low voltage (around 4V) and speed for polishing and add a drop or two onto the wet/dry paper so that most of the paper has a thin layer of water and then start polishing. Surface tension of the tiny "puddle" of water keep things together a lot better than one would expect. I keep an eye on it and as it starts getting dry-ish I add more water. Every few minutes I stop and dry off the water and remove any accumulated material so the grit does not get clogged. Rinse and repeat. Repeatedly... Yes, it is a slow, painful process. But it actually works surprisingly well

[Billy boy]

nice looking gizmo. are you useing an adjustable power supply with your pmt truer? seems to me that 100rpm is far to slow to polish.great engineering though

[HO RacePro]

I do have adjustable power supplies for both machines, although I have only been operating at 12 volts. I picked on a 100 RPM gearmotor just at an educated wild guess. Based on what I've seen so far I was probably far too conservative. I could probably run at much higher RPM's without causing splashing or foaming.

I want to modify my axle-mounted timing pulley so I can use a timing belt rather than an O-ring for the drive. A timing belt should be able to transmit much more power without slipping.

[Brumos RSR]

Hanging Fire…..get off the dime? New to me but I’m stealing both. Meaning: stop procrastinating and take action. Google is definitely my Friend.

[HO RacePro]

I get some comfort from the fact folks confounded by my technish bafflegab can look up those terms on Google. Pre-internet it was something I had to be more careful about.

As for "expressions", it seems I have accumulated many and imported quite a few from deep in the previous century. My wife complains about it -- and she is my age. But they do add color, don't they?

And delay is not always procrastination. Sometimes things get shoved to the back because they lack priority. And sometimes I come up against an issue that doesn't have a good solution -- at least at first. If I let things sit for a bit very often I'll find a way around the problem. A solution can come to me when I'm not really thinking about it. I have learned that trying to force a solution often won't produce one, or if it does, maybe not a good one. So if I'm not really comfortable with the solutions I have I'll put the whole project aside until I get some better ideas.

[Brumos RSR]

You’re 100% correct, slot car guys do not procrastinate, we delay and then take action. 😀😀

[HO RacePro]

A good result yesterday at the IHSR race event. My Carrera Porsche, which has ignominiously finished last in every race to date pulled out a fifth place finish. This in a field where less than half a second per lap separated first from last (seventh) place. The only upgrade to my car was new Carrera "Tuning Tires" trued on my Professor Motor machine and wet-sand polished on my custom-built tire sanding station.

Still a ways to go to move that car to the front, but polished rear tires seemed to help. I've also more work to do on the polishing station, but it seems like I've made some progress.

[4424ever]

It’s nice to taste the fruits of your labour when they’re not lemons!